The present invention relates to a photographic projector, and more particularly to a photographic projector that projects a color image of a relative large original color picture film onto a printing paper with desired magnification to produce an enlarged color print.
Apparatus of this type is known as a photograph enlarger. Enlargers which reproduced a picture image of relatively large color picture original film (for example, a 4.times.5 inch original), typically have a construction based upon that of a process camera which is used in the field of plate printing.
An example of such apparatus is shown in FIGS. 4 and 5. In such apparatus, the photographic projector includes a support member 3 erected at the rear surface 4 of a lower frame 1 which is provided with an easel 2 on its upper surface. An original picture holder 100, which holds an original picture film 7, is mounted to be movable in the vertical direction along a guide rail 4 which is fitted to an appropriate position of the support member 3. The original picture holder 100 includes an original picture frame 6 which holds the original film 7 (hereinafter, refer to "original picture") at a predetermined position, an original picture holder base 5 which couples frame 6 to rail 4 and a lamp housing 8, for accommodating a light source (not shown) which project light through the original picture 7.
Under the original picture frame 6 there is provided a lens holder 110 which is coupled to and movable in the vertical direction along the guide rail 4. The lens holder 110 includes a lens seating plate 10 which supports a lens 11 for projecting light and a lens holder base 9. Between the original picture holder 100 and the lens holder 102 there is provided a bellows 12 for shielding the light.
Rotary encoders 13 and 14 are attached to the bases 5 and 9, respectively. The original picture holder 100 and/or the lens holder 110 are moved, in response to the engagement of gears 15 and 16 secured to each of their axes with a rack 17 erected vertically with respect to the support 3, respecitvely. When either or both of the picture holder 100 or the lens holder 102 are moved, respective pulses are generated according to the distance it (they) move. By counting the number of these pulses, the positions of the original picture holder 100 (and therefor original picture 7) and the lens holder 110 (and therefor lens 11) may be calculated and based on these results, the positions at which the original picture holder 100 and the lens holder 102 are to be located may be controlled. In this manner, the reproduced picture image may be focused with a desired magnification. The magnification can be controlled as a function of the positions of the original picture holder (and therefor picture 7) and the lens holder 102 (and therefor lens 11) based on the following known lens equation; EQU 1/a+1/b=1/f, m=b/a EQU a=f.times.(1+m) EQU b=f.times.1/(1+m)
Wherein:
a: distance between an original picture 7 and the lens 11 (original picture distance)
b: distance between the lens 11 and the focusing plane 2 (picture image distance)
f: focal distance of the lens
m: magnification
Accordingly, there are means which can make them bring more closely with each other by varying appropriately the size of the original picture and that of a desired reproduction picture.
As described above, when the magnification m is obtained as a function of the relative sizes of the original picture and reproduction picture, the positions at which the original picture holder 100 (and therefor picture 7) and the lens holder 102 (and therefor lens 11) should be located can be calculated. For example, when the magnification ratio is 1:1, as shown in FIG. 4, the "original picture distance a" and "the picture image distance b" are both 2.times.f.
However, the range of magnification which this kind of photograph projector can achieve is limited to a range determined by the mechanism of the apparatus. For example, in FIG. 5, there is shown a state in which magnification of the apparatus shown in FIG. 4 is set at 5:1. As shown by arrow A, the lower end portion picture of the picture holder base 5 and the upper edge portion of the lens holder base 9 must overlap at the identified portion to achieve the desired magnification. In the prior art apparatus the bases 5 and 9 would collide with each other before reaching this state. As a result, the range of magnification which can be achieved by this apparatus is less than 5 to 1.
In view of the foregoing, the prior art has proposed the following apparatus to increase the possible magnification levels.
One proposal suggests that the shape of the bases 5 and 6 be modified so that they can approach more closely than they previously could. For example, the under surface of the base 5 and the upper surface of the base 6 may be flattened so that the original picture frame 6 and the lens seating plate 10 may approach a position at which they are nearly in contact with each other.
However, when the size of the bases 5 and 6 are excessively small in the vertical direction, the picture frames 6 and lens seating plate 10 are secured in an unstable manner. As a result, the size of the bases 5 and 9 can not be made smaller than a certain value, and the degree to which either base has been flattening one plane must be compensated for by increasing the size of the reverse side of the base. This is likely to create other drawbacks in the overall structure. That is, if the frame base 5 is extended in the upper direction, the entire height of the supporting rod 4 must be extended to the same degree. If the lens holder base 9 is extended downwardly, the degree to which the lens holder base 9 can be reduced is limited since the base 9 is likely to interfere with the easel plane 2 as the lens holder 10 approaches the easel plane 2 as shown in phantom in FIG. 5. As a result, there are some cases in which a desired picture image focal distance can not be obtained.
One other proposal for making the original picture frame 6 approach to the lens holder 10, makes the width of the lens holder base 9 narrower than that of the original picture holder base 9 and causes the bases 5 and 9 to be moved along different guide rails. The lens holder base 9, is free to move into the inside of the original picture holder base 5. However, in this proposal two sets of guide rails, which are required increases the amount of material required, increasing in the number of assemblies, etc. This increases the cost of the enlarger. Another proposal uses a "convex cone" and a "concave cone". In this arrangement, a small seating plate is detachably mounted on the central portion of the lens holder 10, and as usual the lens 11 is equipped with this small seating plate. However, when large magnification projection is required (in wihch case the original picture frame base 5 may collide with that of the lens holder base 9), the small seating plate is replaced with a concave cone having a cup shape (that is, a cone the central portion of which is concave), and further the lens 11 is equipped with the bottom of the concave cove. By this arrangement, the original picture may be brought close to the lens 11 than is possible with the use of the standard seating plate and a focused picture image having any desired large modification is obtained. When a reduced magnification projection is required, the convex cone is used.
In this arrangement, there is no need to apply any particular modification to the original picture frame and the lens holder bases 5, 9. It is only necessary to modify the lens seating plate 10, so that this arrangement can be realized relatively easily. However, the position at which the lens 11 is fixed differs from that when a standard lens seating plate is used, so that when the lens 11 is to be focused, it is necessary to compensate for this difference. Particularly, in such apparatus which is provided with an auto focusing means as shown in FIG. 4, because the auto focusing means is adapted to control the position of the lens holder 110 according to the number of pulses generated from a rotary encoder 14, if the position of the lens relative to the lens holder 110 is changed, the enlarger will be out of focus. In order to compensate for this variation in lens position, it is necessary to discriminate operation data depending on whether or not the adapter is being used. This is quite inconvenient.
In addition, in practical use the standard lens seating plate 10 and the concave cone or the convex cone must be exchanged. As a function of the desired magnification value these exchanges require troublesome work.